Propeller induced vibratory forces acting on the rudder of a water tunnel simulation of the SEA CONTROL SHIP are measured as a function of longitudinal and transverse clearance in order to determine an optimum location. The influence of propeller-rudder clearance on steady state propulsion and rudder effectiveness is obtained. It is found that vibratory forces measured at a cavitation number corresponding to full power are three times the corresponding values measured without cavitation. A significant reduction in vibratory force at zero rudder angle appears to be possible by moving the rudder from the present design location. The present transverse propeller-rudder clearance appears to be optimum.